Cigarette dense end monitoring and controlling apparatus

ABSTRACT

A dense-end monitor and controller is provided for a cigarettemaking machine of the dense-ending type. In a preferred embodiment, a density gauge is positioned adjacent to the moving cigarette rod for providing a first signal varying with the occurrences of dense portions in the tobacco rod. Another signal is supplied for each cutting action of the rod cutter by means synchronized to the rod cutter. Correlation waveform generators generate sawtooth and triangular-shaped waveforms which are phase-synchronized with the dense portion pulses in the density gauge signal. Two output signals, one representing deviation of the dense portions from their proper position at the ends of the cut cigarettes, and the other representing the relative increase in the amount of tobacco in the dense portions, are provided for visual display and machine control purposes. The signals are obtained by correlating the density signal with the triangularshaped waveform and by sampling the sawtooth-shaped waveform at the instant the cutter signal is generated. The output signals are free of any interdependence of information content.

United States Patent [191 Lipcon et al. July 3, 1973 1 CIGARETTE DENSEEND MONITORING AND CONTROLLING APPARATUS [57] ABSTRACT PrimaryExaminerFrank T. Yost Attorney-William T. Fryer et al.

[75] Inventors: Jesse B. Lipcon; James N. Horn, both of Columbus, Ohio[73] Assignee: Industrial Nucleonics Corporation, Columbus, Ohio [22]Filed: Mar. 15, 1972 [21] Appl. No.: 234,767

[52] US. Cl 83/13, 83/72, 83/76, 83/360, 83/361, 83/522, 13l/21 R,131/21 B '[51] Int. Cl. A24c 5/32 [58] Field of Search 83/13, 72, 74,76, 83/360, 361, 370, 522; 131/21 B, 21 R, 22 R, 63, 65, 46

[56] References Cited UNITED STATES PATENTS 3,066,562 12/1962 Barnett etal. 8 3/74 3,604,429 9/1971 DeWitt 131/21 B 3,604,430 Norwich et al131/21 B A dense-end monitor and controller is provided for acigarette-making machine of the dense-ending type. In a preferredembodiment, a density gauge is positioned adjacent to the movingcigarette rod for providing a first signal varying with the occurrencesof dense portions in the tobacco rod. Another signal is supplied foreach cutting action of the rod cutter by means synchronized to the rodcutter. Correlation waveform generators generate sawtooth andtriangular-shaped waveforms which are phase-synchronized with the denseportion pulses in the density gauge signal. Two output signals, onerepresenting deviation of the dense portions from their proper positionat the ends of the cut cigarettes, and the other representing therelative increase in the amount of tobacco in the dense portions, areprovided for visual display and machine control purposes. The signalsare obtained by correlating the density signal with thetriangular-shaped waveform and by sampling the sawtooth-shaped waveformat the instant the cutter signal is generated. The output signals arefree of any interdependence of information content.

21 Claims, 5 Drawing Figures A I 22 FORMER O DENSITY MEASURE RE E 3SIGNAL PEAKS s2 PULSE GENERATOR 4 PHASE ERROR SIGNAL $3 I as FIRST 63SIGNAL e ifi g' i MULTIPLIER A E A 66\ GENERATOR MEANS PHASE- FREQUENCYso SYNCHRONIZER SECOND 62 R CUTTER ggkggfi' MULTIPLIER PBIEgIASLSIGENERATOR %DENSE-ENDING PHASE ANGLE PATENTED JUL 3 I975 SHEU 0F 3TRIANGULAR CORRELATING WAVE FORM PEAK S2 I DENSITY SIGNAL: I

FIG. 3a

I DENSITY I SIGNAL PEAK 52 k-ZERO-CROSSING POINT T SAWTOOTH 3bCORRELATING WAVEFORM CUTTING SIGNAL PULSE g zERo-cRoss|NG I POINT TSAWTOOTH I .3 CORRELATING FG C WAVEFORM CIGARETTE DENSE END MONITORINGAND CONTROLLING APPARATUS BACKGROUND It is well known in thecigarette-making art to manufacture cigarettes having increased amountsof tobacco in the regions adjacent to the cut ends. The purpose of thisprocess, known as dense ending, is to give the cigarette a superiorappearance, a firm feel to the touch, and to prevent loosely-packedtobacco from falling out of the cigarette ends.

Dense-ending devices are a part of many contemporary cigarette makersand they may take on various forms. For example, compacting members maybe used to periodically compress the tobacco stream ahead of atrimmer,extra charges of tobacco may be placed at intervals in the tobaccostream, a special rotating trimmer wheel having peripheral indentationsmay be used to trim off more tobacco in certain spaced regions of thetobacco rod than in others, or a tobacco-conveying belt may be providedwith perforations corresponding to the desired density pattern to enableair to be drawn therethrough, arranging the tobacco filler in thedesired dense-end pattern. U.S. Pat. Nos. 1,920,708, issued Aug. 1,1933, and 3,306,305, issued Feb. 28, 1967, both to D. W. Molins,1,968,018, issued July 31, 1934 to C. Arelt, and 3,032,041, issued May1, 1962, to R. Lanore, are representative of the state of the art.

In cigarette-making machines utilizing dense enders, serious problemsarise when the occurrences of the dense ends in the tobacco stream getout of synchronization with the cigarette cutter. Normally, thedenseending device is synchronized with the cutter so that the cutoccurs approximately in the center of the dense regions. However, it issometimes desired to offset the dense-end regions from the location ofthe cut end, as for example where the leading ends of non-filtercigarettes are densed for the purpose of compensating for weight lossesdue to deceleration forces. The cutter is often located several feetdownstream from the denseending device, so that unpredictablecompression or stretching of the tobacco stream which forms thecigarette rod may occur, sometimes as a function of machined speed,causing an out-of-synchronization condition such that dense regions canappear in portions of the cigarette other than the desired portions.

Modern cigarette makers have a production rate of between 1,000 and4,000 cigarettes per minute, so that careful and accurate monitoring ofcigarette quality is necessary to prevent wasted tobacco, or wasted timewhere low-quality cigarettes have to be reprocessed. Manual inspectionis impractical because of the need to sample a large number ofcigarettes, and because it is virtually impossible to discriminatebetween a lowquality condition resulting from loss of denseend/cuttersynchronization and one resulting from a decrease in the density of thedense regions. Likewise, manual inspection may overlook cigarettes inanoverdensed condition, which are not free on the draw" and areexpensive to make.

Two prior dense-end measuring and controlling devices are described inU.S. Pat. No. 3,604,429, issued Sept. 14, 1971, to John E. DeWitt andU.S. Pat. No. 3,604,430, issued Sept. 14, 1971, to Alan Norwich et al.,both assigned to the same assignee as the present invention. Accordingto these patents, in general, information is obtained as to the relativeposition of the dense-end region and the cigarette end. In oneembodiment, a gauge is positioned adjacent to the moving cigarette rodfor measuring the weight per unit length or density of the dense-endregions, and a reference signal synchronized to the operation of thecutter is generated for comparison with the output of the density gauge.In one approach these signals are utilized to provide an oscilloscopedisplay. However, the oscilloscope display, in the embodiment disclosed,is somewhat difficult to set up and interpret by cigarette-makingmachine operating personnel without extensive training. In another form,these signals are utilized to produce continuous electrical outputsignals for indicating, as by the deflection on one or two meters, theposition and relative density of the dense ends. Where separate outputsignals are provided according to the prior embodiments, there may be aninterdependence of the signals such that, unless the dense ends occur inproper phase with the cutter, the signal which indicates the position ofthe dense ends is affected by their relative density, and the signalwhich indicates their relative density is affected by their position.Also, the use of a simple square waveform for the reference signal hascaused difficulty in obtaining the desired degree of accuracy, since, ifthe reference signal pulse length is not the same as the length of thedense-end pulse, the denseend position output signal has a dead signalrange around the point of perfect synchronization.

The present invention solves the problem of how to prevent phase angleinformation from intruding into the percent density signal and viceversa, as will be apparent from a reading of the description whichfollows.

SUMMARY OF THE INVENTION regions ascompared with the non-dense regions,thus offering a reliable real-time check on the desired relative densityof the dense regions, which may be, for example, 10 percent, 15 percent,or 20 percent over the density of the remainder of the tobacco rod.Moreover, the apparatus according to the invention provides outputswhich may in addition be used to exert feedback control over thecigarette-maker to correct maladjustments in the process automatically.

According to one specific embodiment, a gauge is positioned adjacent tothe moving cigarette rod. This gauge provides an output signalindicative of the weight per unit length of the cigarette rod. Thesignal includes recurrent component peaks representative of the denseregions in the cigarette rod. A reference pulse generator synchronizedto the action of the cutter produces another periodically varyingsignal. Two correlating waveform generators are provided to produce twodifferent correlating waveforms in response to timing pulses from aphase-frequency synchronizing means. One correlating waveform issymmetrical, or even, about the periodically occuring peak whichrepresents the location of the dense region. The other correlatingwaveform is asymmetrical, or odd, about the location of the densitypeak. The phase-frequency synchronizer causes these correlatingwaveforms to be generated at the frequency of the cutter signal pulse.

The even correlating waveform is correlated with the density signal by amultiplying means, and the product is averaged and read into a visualdisplay means to provide a percent dense-ending indication. The oddcorrelating waveform is correlated with the density signal in anothermultiplying means. The product is averaged, and the average is fed backas a phase error signal to the phase-frequency synchronizer. This phaseerror signal will be zero if the phase of the correlating waveforms isidentical to the phase of the dense region peaks in the density signal.Should the correlating waveforms be out of phase with the peaks in thedensity signal, the phase error signal will have a polarity dependent onthe direction of the phase displacement and a magnitude directlyproportional to the amount of phase displacement. The phase error signalcauses the phasefrequency synchronizer to adjust its timing pulses sothat the correlating waveforms are again in phase with the densitysignal peaks, reducing the phase error signal to zero. Thus thephase-frequency synchronizer means delivers a timing pulse to thecorrelating waveform generators at the frequency of the cutter pulse andat a phase which causes the correlating waveforms to be in phase withthe density signal peaks. A phase angle signal suitable for operating avisual display device is derived by a sample-and-hold circuit which isresponsive to the same correlating waveform that generates the phaseerror signal. The sample-and-hold circuit is gated by the cutter signal.

The present invention solves the problem of how to prevent phase angleinformation from intruding into the percent density signal and viceversa. It accomplishes this, in a preferred embodiment, by generatingone or more reference correlating waveforms, having a frequencyidentical with that of the cutter signal, while being in exactphase-synchronization with the dense-end peaks in the density gaugesignal. In this manner, with the phase error between the correlatingwaveforms and dense-end peak maintained at zero, the output signalrepresenting percent dense-ending is directly proportional to theaverage amount of the increase in the cigarette weight per unit lengthcaused by the extra tobacco in the dense ends and is independent of thedisplacement of the dense regions from the cut ends of the cigarettes.To obtain the displacement or phase angle output, the appropriatereference correlation waveform is sampled at the instant of cutting,giving either a positive or negative signal representative of theposition of the cut ends with respect to the average position of thedense regions.

OBJECTS OF THE INVENTION Accordingly, it is an object of the presentinvention to provide an improved dense-end monitor which generatesoutput signals indicative of cutter/dense-end synchronization and of therelative increase in density of the tobacco in the dense regions of thetobacco rod, which signals are free of any mutual dependence.

It is another object of the present invention to provide an improveddense-end monitor in which, by a proper choice of correlating waveforms,the output signals are linear with respect to changes in cutter/denseendsynchronization and percent dense-ending, and do not have dead signal"portions.

Further objects and advantages will become apparent from the followingdetailed description of preferred apparatus according to the invention,taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a schematic showing of acigarette-making machine in combination with an improved dense-endmonitoring and control system according to the invention.

FIG. 2 is a more detailed schematic drawing of the improved dense-endmonitoring and control system of FIG. 1.

FIG. 3a is a graph showing waveforms depicting the condition of perfectphase synchronization between one preferred correlating waveform and thedensity signal.

FIG. 3b is another graph depicting the condition of perfect phasesynchronization between the other preferred correlating waveform and thedensity signal.

FIG. 3c is another graph depicting the condition of perfect phasesynchronization between the other preferred correlating waveform and thecutting signal pulse.

CIGARETTE DENSE-ENDING PROCESS With reference now to the drawings andparticularly to FIG. 1, a typical cigarette-making machine includes atobacco stream former l0 delivering a stream of tobacco 12 to a rodformer 14. Here, a paper strip 16 is wrapped around the tobacco stream12, and the seam is glued to form a cigarette rod 18. The cigarette rod18 passes on to a cutter 20 which periodically cuts a cigarette 22 oflength L from the continuous rod 18. Conventionally, the cigarette rodis measured and the machine is controlled to provide cigarettes having adesired weight per unit length.

A dense-ending device 24 may be built onto the cigarette-making machineto provide regions of higher relative density in the tobacco stream.These devices may take on various forms as stated above. As seen in FIG.1, a rotating trimmer disc 24 trims off some tobacco 12a which isreturned upstream leaving an excess amount of tobacco in dense regions Rof the tobacco stream fed to rod former 14. The dense regions are spacedone cigarette length L apart from one another for non-filter cigarettesand a distance 2L for filter cigarettes. Where the tobacco stream hasbeen wrapped to form the rod 18, which is of relatively constantdiameter, the density of the tobacco in the dense regions of thecigarette rod may be up to 30 percent greater than the density in theremainder of the rod. As a typical example, the length of the denseregion R may be 10 to 20 millimeters for a cigarette millimeters inoverall length.

A main drive motor 26 provides motive power for simultaneously conveyingthe cigarette rod 18 toward the cutter 20 and actuating the cutter 20 tocut cigarettes of substantially equal length from the rod 18. Thedense-ending device 24 is also coupled via differential drive unit 48 tothe main drive motor 26 as indicated by the dotted line 28. The purposeof the differential drive unit 48 is to time the dense-ending device 24with the cutter 20, so that the cutter cuts the tobacco rod 18substantially in the center of each dense region R.

If, clue to the longitudinal dimensional changes of the tobacco stream12 or rod 18 or slippage of the drive to either the cutter 20 or thedense-ending device 24, the cutter and dense regions R are not insynchronism, the cigarettes 22 will either have an excessive or aninsufficient amount of tobacco at one end or the other, or they may lackdense ends entirely.

For non-filter cigarettes, when the rod 18 is properly cut substantiallyin the center of each dense region, one end of the cigarette 22 containsapproximately the same amount of extra tobacco as the other end. Toaccomplish this result, one must know the position of the dense regionswith reference to the cut ends of the cigarettes to determine whetherthe cutter is properly synchronized, and, if it is not synchronized, theamount and direction in which it is out of synchronization. For filtercigarettes, in which only the open end is densed, the tobacco rod 18 iscut both through the center of each dense region R (a distance 2L apart)and through the midpoint between adjacent dense regions R. In this case,the occurrence of each dense region R is compared with every othercutting stroke, as explained in more detail below.

DENSE-END MONITOR AND CONTROL The dense-end monitor includes a gauge 30located upstream from the cutter 20 to measure the density of the rod18. It may be of any well known type which measures the weight per unitlength or density of the cigarette rod. A cutter reference pulsegenerator 32 is synchronized to the action of the cutter throughmechanical, electrical, photoelectric, magnetic, or other equivalentmeans well known to those skilled in the art. In addition to generatingcutter pulses Sl, generator 32 provides a fixed number of segment pulsesS1 per cigarette, for purposes to be explained below. According to thepreferred embodiment, six segment pulses are generated per cigarette inessentially the same manner as the cutter pulses. Both types of pulsesare amplified and shaped by appropriate circuitry in pulse generator 32.In a simpler form, reference pulse generator 32 may consist of one ormore switch contacts which close every time a cigarette 22 is cut fromthe rod 18.

Two correlating waveform generators 60 and 61 are provided forgenerating correlating waveforms of differing types to be compared withthe density signal peaks S2 and the cutter signal pulses S1 to give apercentage dense-end reading and a phase-angle reading, respectively.The correlating waveforms are preferably triangular and sawtoothwaveforms generated by conventional waveform generators, although otherwaveforms can be used. Correlating waveform generator 61 generates thesawtooth waveform, and correlating waveform generator 60 generates thetriangular waveform. These waveform generators are set up to betriggered at the frequency of the cutter signal pulses Sl by means of aphase-frequency synchronizer 66. Phasefrequency synchronizer 66 alsomaintains the phase of the correlating waveforms in synchronism with thephase of the density signal.

' Referring to FIG. 1, the density signal and the even correlatingwaveform output of generator 60 are correlated in multiplier 62,yielding a signal which is averaged in an averaging circuit 64 and fedinto a visual display means, such as a meter 40. A cigarette-makingmachine operator monitoring the visual display 40 is thus provided witha continuous reading representative of the relative increase in tobaccoin the dense regions R. The instantaneous value of the odd correlatingwaveform output of generator 6] is sampled at the in stant the cuttersignal pulse S] is generated, by means of a sample-and-hold circuit 67,whose output is fed into a visual display means comprising a meter 41 toindicate to the operator whether the dense region R is being positionedin the rod 18 such that the cutter 20 will pass through the center ofthe dense region R, and if not, the amount and direction of thedeviation of the dense regions R from the cut ends.

The operator can thereby make appropriate adjustments to the machine tocorrect the faulty dense-end condition. Alternatively, automatic controlcan be exerted by means of a suitable controller device 46 operatingdirectly from the phase angle signal T1, as described below.

Multipliers 62 and 63, which perform the correlation functions, mayassume various forms, the proper selection of which will be apparent toone skilled in the art. For example, each multiplier may be a trueanalog multiplier (Hall effect, transistor or integrated-circuittransconductance, Field effect, duty-cycle, etc.). It may be adigital-to-analog type of hybrid multiplier, if the correlation waveformis in digital form. Or it may be a pseudomultiplier or multiplier-likecircuit, such as an analog gate, synchronous demodulator, or the like.In the preferred embodiment, multipliers 62 and 63 are of the trueanalog multiplier type.

CORRELATING WAVEFORMS The proper choice of correlating waveform isdependent upon the desired form of output signal to be obtained from themultiplication process. Because a zero phase angle signal is desired forthe condition of perfect cutter/dense-end synchronization, withpositive-going and negative-going signals representing lead or lag, acorrelation waveform having essentially a constant slope from l to ispreferred. It is to be understood that each l80 to +l80 cyclecorresponds to the time required for one cigarette length to pass agiven point, for example the location of gauge 30. See FIG. 3c. Such awaveform may be described as an asymmetrical or odd waveform and definedby the equation f(t)-f(-t), with the origin of the time t and f(t)reference axes being positioned midway along the slope between thelowest and highest points of the waveform. See FIG. 3b. The oddcorrelation waveform is normally phase-synchronized to the densitysignal peak S2, such that itsf(t) reference axis eoincideswith thecenter of the density peak S2. In other words, this correlation waveformis odd with respect to the density peak S2. The point midway along thewaveform slope is arranged to be at zero or ground potential, and it isfrom this point, the so-called zero-crossing point," that deviations ofthe positions of the density signal peak and the cutting signal pulseare measured. When the zero-crossing point of the sawtooth correlatingwaveform is exactly in phase with the density signal peak S2, azero-valued phase error feedback signal S3 will result. Similarly, whenthe zero-crossing point of the sawtooth waveform is exactly in phasewith the cutting signal pulse 81, a zero-valued phase angle outputsignal T1 will result.

With respect to density information, an output signal having a magnitudedirectly proportional to the amplitude of the density signal peak isdesired. Thus a correlation waveform which is symmetrical about areference axisf(t) drawn through the average position of the positivepeak is preferred. Such a waveform may be described as a symmetrical oreven waveform and defined by the equation f(t)=+f(t), with the f(t)reference axis passing through the positive peak and the t referenceaxis passing through points midway along the slopes between the highestand lowest points of the waveform. See FIG. 30. When the evencorrelation waveform is in phase with the density signal peak S2, itsf(t) reference axis coincides with the center of the density peak S2,and the correlation waveform is said to be even about the density peakS2. The even waveform generator is arranged so that the t reference axisis at ground potential and passes through the points midway along thewaveform slope. When a correlation waveform of this approximate shape ismultiplied with a non-zero density signal, the resulting product will bea positive, non-zero output signal directly proportional to themagnitude of the percent dense-ending factor. Thus, when the positivepeak of the triangular correlating waveform is exactly in phase with thepeak S2 in the density signal, their product will yield an output signaldirectly proportional to the percent dense-ending.

While the preferred correlating waveforms may be described ratherprecisely by the above equations in terms of functionsf(t) and f(t)about a selected reference axis, waveforms having only the generalcharacteristics of the above-described correlating waveforms may be usedas equivalents. That is, a waveform fitting neither of the equationsf(t)=f(t) or flt)=f(t) precisely may nevertheless be equivalent ingeneral shape and in function to one or the other preferred correlatingwaveforms. The appearance of the correlating waveforms can be describedeither by smooth, continuous curves or by discrete levels or steps.Examples of the former are ramp, sawtooth, triangular, sinusoidal, andsimilar waveforms. In the latter category, waveforms consisting of oneor more discrete levels may be generated by any well known on/off,stepping, counting, or other digital circuit. By way of illustration, adigital up/down counter may be used to provide an incrementallyincreasing and decreasing periodic signal resembling a triangular-shapedwaveform.

PHASE-FREQUENCY SYNCHRONIZER The phase-frequency synchronizer 66performs a dual function, in that it triggers the correlation waveformgenerators 60 and 61 at the frequency of the cutter signal pulses S1,while maintaining the phase of the correlation waveforms in exactsynchronization with the phase of the density signal peaks S2. As to thelatter function, the phase-frequency synchronizer 66 acts in thecapacity of a variable phase delay, by either advancing or retarding thephase of the correlation waveforms with respect to the phase of thedensity signal peaks S2.

Referring now to FIG. 2, a more detailed schematic of the structurecomprising the phase-frequency synchronizer 66 as it appears in thepreferred embodiment is shown. An up/down counter 102 is provided forstoring an arbitrary eight-bit number C to C The up/- down counter 102is an eight-bit register, whose input lines are driven byvoltage-controlled oscillators 101 and 103. Cycling counter 104 is aneight-bit counter, whose outputs are A to A Cycling counter 104 isdriven by a voltage-controlled oscillator (VCO) 106, which is responsiveto the cutter signal pulse S1, such that cycling counter 104 makes onecomplete 00000000 through 1 ll 1 l 1 ll cycle during the time eachcigarette passes the gauge 30. A digital comparator is provided fordelivering a synchronizing pulse exactly once per cigarette when theeight-bit number A generated by cycling counter 104 coincides with theeight-bit number C stored in up/down counter 102. The A=C output pulseof comparator 100, occurring once per cigarette, is the basic timingreference for the correlation waveform generators 60 and 61.

A phase detector 108 and VCO 106, cooperate with cycling counter 104 toform a phase-locked loop, such that the cycling counter 104 completes afull 00000000 through 11111111 counting cycle between successive cuttersignal pulses. The most significant bit A in cycling counter 104 is fedback as one input to the phase detector 108. Phase detector 108 maysupply a positive or negative output, corresponding to a lag or leadcondition of A with respect to the cutter signal pulse, to integrator107 whose output in turn drives the VCO 106. For example, if theoccurrence of the most significant bit A lags the cutter signal pulse, apositive output is supplied to integrator 107 for an amount of timedependent upon the amount of lag, causing the integrator 107 output togo more negative, thereby causing a higher frequency output from VCO106. Likewise, if the A Comparison pulse occurs too soon, phase detector108 supplies a negative output for an amount of time dependent upon theamount of lead, causing the VCO 106 output to go less negative, therebycommanding a lower frequency. These positive and negative-going signalscontrol the output frequency of VCO 106 in such a manner as to maintainthe A 1 to 0 transition coincident with the cutting signal pulse.

In normal operation, with the phase-locked loop in the locked condition,the A 1 to 0 transition occurs very close to the time of the cuttingsignal pulse. How ever, phase errors can occur because of electronicnoise, integrator input leakage currents, and speed changes in thecigarette-making machinery. The combined effect of these errors is tocause very small corrections to occur in either direction. Thus, at theinstant of the cutting signal reference pulse, there will be a veryshort positive or negative-going correction output pulse from phasedetector 108.

The variable eight-bit number C to C in up/down counter 102 is comparedwith all the eight-bit numbers generated during the 00000000 to l l l 111 l 1 transition of cycling counter 104, by means of the digitalcomparator 100 to provide a coincidence pulse A=C exactly once duringeach cigarette period. For a relatively lower number in up/down counter102, the A=C coincidence pulse will occur relatively sooner during thetransition cycle of cycling counter 104. Conversely, a relatively higherreference number in up/down counter 102 will occasion a relatively laterA=C coincidence pulse.

In order to advance or retard the occurrence of the A=C correlationwaveform triggering pulse, a phase error signal S3, representative ofany phase difference between the correlating waveforms and the dense endpeaks S2, is applied to the phase-frequency synchronizer 66. Because thecorrelating waveform generators are triggered simultaneously, theirrespective waveforms are automatically in phase-synchronization witheach other. It is necessary, therefore, to compare the phase of only oneselected correlating waveform with the phase of the dense end peaks S2.In the preferred embodiment, the sawtooth correlating waveform isselected for this phase comparison process, since the phase error signalS3 will be zero when the density signal peak S2 coincides with thezero-crossing of the sawtooth waveform, as seen in FIG. 3b. Thus, withreference to FIG. 2, the sawtooth correlating waveform is compared withthe phase of the dense end peaks S2 by means of the multiplying circuit63, and theresultant signal is averaged in the averaging means 65. Phaseerror signal S3 brings about either an increase or a decrease in thevariable number C in up/down counter 102, by means of thevoltage-controlled oscillators 101 and 103. Voltage-controlledoscillators 101 and 103, as well as 106, are well-known electroniccircuits for generating output signals at a frequency directlyproportional to the magnitude of the voltage input. For an input ofpositive polarity or for no input at all, VCO 101 and VCO 103 generateno output. For a negative voltage input, they generate pulses at afrequency which is directly proportional to the magnitude of the inputsignal.

When the zero-crossing point T of the sawtooth correlating waveform(FIG. coincides with the center of the density peak S2, the averagevalue of their product is zero, and no change is effected in thereference number C stored in up/down counter 102. Should thezero-crossing point T stray from the center of the density peak, eithera positive or negative DC voltage results, in the form of the phaseerror signal S3, thereby causing either VCO 103 or VCD 101,respectively, to generate pulses which step up or step down thereference number stored in up/down counter 102. For example, if thezero-crossing point T leads the center of the density peak S2, theaverage value of the product of the two waveforms is a positive DC phaseerror voltage. The positive voltage prevents VCO 101 from operating.However, the positive input to inverter 105 results in a negative outputtherefrom, causing VCO 103 to put out pulses at a repetition rateproportional to the magnitude of the error. These pulses cause the up/-down counter 102 to count up, gradually bringing the sawtoothcorrelation waveform into phase equilibrium with the density signal, atwhich point the phase error voltage is again zero. If the zeroecrossingpoint T lags the occurrence of the density signal peak, a negative DCphase error voltage appears at the output of averaging means 65, causingVCO 101 to step down the reference number in up/down counter 102 untilphase equilibrium is reached. The inverter 105 at this time applies apositive voltage to VCD 103, keeping it turned off.

CORRELATION AND OUTPUT Because of the synchronizing action of the phaseerror control loop, the zero-crossing point T of the sawtoothcorrelating waveform tracks the position of the dense end peak S2. Thetriangular correlating waveform is also synchronized with the sawtoothcorrelating waveform, so that the positive peak of the triangularwaveform coincides with the zero-crossing point T of the sawtoothwaveform. In one embodiment of the dense end monitor which has beenconstructed, this was done by using the sawtooth waveform to generatethe triangular waveform. The sawtooth voltage, taken with reference toground, was applied to a conventional absolute value circuit having again of 2, with the absolute value of the sawtooth voltage effectivelysubtracted from a fixed constant voltage to yield the correspondingvalue of the triangular waveform. The sawtooth waveform can also begenerated by using, say, a conventional eight-bit digital up counterresponsive to VCO 106 and being reset by the A=C pulse. The triangularwaveform is again generated from the sawtooth waveform by using the00000000 through 0] l l l I ll portion of the counting cycle to generatethe up" slope of the triangular waveform and the l0000000 through 11111111 portion to generate the down slope. A conventional digital-to-analogarrangement is used for generating a voltage proportional to the pulsecounts. Thus, with the zero-crossing T of the sawtooth correlatingwaveform tracking the dense-end pulse $2, the positive peak of thetriangular waveform also tracks the dense-end pulse. Therefore, when thetriangular correlating waveform is multiplied in the multiplying circuit62 by the density signal, and averaged over time in the averagingcircuit 64, the resulting voltage is directly proportional to themagnitude of the percent dense-end signal. This signal will always beindependent of phase angle due to the fact that the positive peak of thetriangular correlating waveform has been synchronized to coincide withthe dense-end peak.

The output voltage representative of the degree of dense-ending isapplied to meter 40 to give a reading representing percent dense-end orquality. In addition, the percent dense-ending output voltage iscompared with an adjustable limit 112, which can be preset by themachine operator to the desired degree of percent dense-eriding, bymeans of limit comparing means 113. A green light 114 is held on bymeans 113 so long as the percent dense-end signal equals or exceeds thedesired limit, while a red light 116, representing low quality, isswitched on if the percent dense-ending output goes below the desiredlimit.

Referring now to FIG. 30, if the sawtooth correlating waveform issubjected to a sample-and-hold operation at the time of the cuttingsignal pulse, a voltage is obtained which is proportional to the phaseangle difference between the cutting signal pulse and the denseendpulse. This output voltage will be zero when the occurrence of thedense-end regions is synchronized with the cutter. A positive phaseangle voltage results when the cutting pulse lags the dense-end pulse,and a negative phase angle voltage results when it leads the denseendpulse. The magnitude of the positive or negative signal is proportionalto the amount of phase angle difference alone, independent of themagnitude of the dense-end pulse. The phase angle voltage is applied toa suitable readout device such as a meter 41. According to oneembodiment of the invention which has been constructed and tested, thephase angle voltage is amplified, inverted, and filtered with a 6-secondtime constant before it is applied to visual display meter 41, providingthe machine operator with a true average indication of the phaserelationship between the cutter and the dense-end regions.

Output signal Tl, representing the direction and magnitude of any phaseerror between the cutter 20 and the dense regions R, is especiallyuseful in controlling the cigarette-making process to maintain propersynchronization. For example, phase angle meter 41 may be a center-zerometer, calibrated in degrees or in millimeters, for the purposes ofshowing immediately to operating personnel the amount and direction bywhich the occurrences of the dense regions R must be shifted relative tothe operation of the cutter 20. Such corrections may be made manually byretiming the denseending means to achieve perfect synchronization.Alternatively, automatic control can be exerted by means of a suitablecontroller 46 operating from the phase angle output signal Tl. Adifferential gearing unit 48 couples the main drive motor 26simultaneously to the cutter 20 and the dense-ending device 24.Differential 48 is provided with a pair of output shafts 50 and 52,whose relative angular position can be adjusted by means of thecontroller 46. Controller 46 is coupled to the control shaft ofdifferential unit 48 by the heavy dotted line 54. U.S. Pat. No.3,306,305, supra, discloses a dense-ending device employing differentialgearing to maintain dense-end/cutter synchronization. Other mechanismsfor effecting automatic control of dense-end/cutter synchronization willbe apparent to those skilled in the art.

Output signal T2, representing the percentage of increased tobaccodensity in the dense regions R, may similarly be applied to a meter 40,calibrated in percent increase in tobacco density or in milligrams.Alternatively, the quality signal T2 may be used as part of an automaticcontrol over the percent increase in tobacco density in the denseregions R, where the nature of the cigarette-making machinery wouldallow it.

The above description of the invention is equally applicable to thedense-ending of filter or non-filter cigarettes. Reference pulsegenerator 32 supplies the cutter signal reference pulse S1 for eachcutting of the cigarette rod, such cuttings normally occurring adistance L apart. In the case of non-filter cigarettes, each cut is madein the center of a dense region R. in the case of filter cigaretteshaving only one end densed, but both ends cut, cutter signal pulses aregenerated at both the densed and undensed cut ends, and it is necessaryto select the cutter signal corresponding to the densed end as thereference pulse S1.

FREQUENCY FEED-FORWARD CIRCUIT To insure that the phase-locked loopcircuit 109 will respond to changes in the cutter signal frequencyresulting .from substantial changes in cigarette maker speed as well asfrom slight speed fluctuations, a frequency feed-forward circuit 111 isincluded as part of the phase-locked loop. This circuit assumes thelarger share of the burden of providing the DC command voltage to VCO106, thereby requiring the phase-locked loop circuit 109 to provide onlya much smaller correction voltage needed in order to maintain perfectphase-synchronization between the A 1 to 0 transition from cyclingcounter 104 and the cutter signal pulse S1. The frequency feed-forwardcircuit reduces considerably the amount of the required to achieve aphaselocked condition and in tracking the small frequency fluctuationsin the cutter signal pulse train. However, it may be omitted at theoption of one practicing the invention, with-out destroying the functionor utility of the device.

The frequency feed-forward circuit 11'] comprises a frequency-to-voltageconverter 110, whose output to.-

gether with the command voltage of integrator 107, is applied to VCO106, which includes conventional circuit means for algebraically summingthe two voltages. Although converter must have a fast response, no greataccuracy is required since reasonable errors in frequency to voltageconversion are corrected by the phase-locking circuit. The input to thefrequency-tovoltage converter 110 consists of a segment pulse train, asdescribed above, synchronized with the reference pulse train and havinga frequency six or [2 times as high. There are six segment pulses percutter reference pulse for non-filter cigarettes, while there are 12segment pulses per cutter reference pulse for filter cigarettes.

Because there are either six or 12 segment pulses per cutter signalpulse, depending upon whether filter or non-filter cigarettes are beingmade, and since the frequency feed-forward circuit 111 delivers acommand voltage proportional to the frequency of the pulses in thesegment pulse train S1, provision must be made to allow for a scalingdifference in VCO 106. This function is performed by a scaling circuit123, including a switch 121 which may be connected to ground asindicated by the dotted line. For non-filter cigarettes, having bothends densed, there are six segment pulses per cutter signal pulse, andswitch 121 is connected to the output voltage V of thefrequency-to-voltage converter 110. For filter cigarettes, with only oneend densed, but both ends cut, there are 12 segment pulses generated"between the occurrences of the dense regions R. In order to maintainthe cycling rate of cycling counter 104 at one complete cycle betweenthe occurrence of consecutive dense regions R, the oscillation rate ofVCO 106 must be halved. This is accomplished by connecting switch member121 to ground, thereby halving the voltage applied to VCO 106 from thefrequency-feed-forward circuit 111.

While one specific embodiment of the invention has been illustrated anddescribed, with a number of modifications suggested, many othermodifications may be made thereto, as will be apparent to those skilledin the art, without departing from the true spirit and scope of theinvention as set forth in the appended claims. Thus, for example, whilethe preferred embodiment of the invention provides separate outputs forboth percent dense-ending and for dense-end/cutter synchronization, theinvention may be practiced by providing only one or the other form ofoutput signal. Thus, the even waveform generator 60, multiplier 62,averaging means 64, and display means 40, including the limitcomparisoncircuitry associated with the present denseend signal T2 may be omitted,should one desire only the display and control signal relating todenseend/cutter synchronization. Likewise, the sample-andhold circuit 67and display means 41, associated with the dense-end/cuttersynchronization output signal T1 may be omitted, should be desire onlythe display and control signal relating to percent dense-ending.

We claim:

1. The method of producing an improved output response from a cigarettedense-end monitor, said monitor having means for measuring thevariations in density along the length of a rod of tobacco havinglocally dense regions spaced along said length for providing a densitysignal having recurrently varying portions corresponding to said denseregions in said rod, means for generating a recurrent signal waveformresponsive to the operation of a cutter which periodically cuts said rodto form individual cigarettes, and means responsive to said recurrentwaveform and to said density signal for providing said output responsewhich is indicative of a characteristic of said dense regions,vsaidmethod comprising adjusting the phase of one of said recurrent waveformand density signals in response to the recurrent waveform and densitysignals so that said signals will have a predetermined phaserelationship irrespective of the position of said dense regions withrespect to said cutter at the instant the rod is cut.

2 The method of monitoring the operation of a machine for producingcigarettes with dense ends, said machine having means for forming atobacco rod with locally dense regions spaced along its length and meansfor conveying said rod past a cutter for severing said rod into aplurality of cigarettes, said method comprising the steps of measuringthe variations in density of said rod along its length to produce adensity signal having recurrently varying portions thereof correspondingto said dense regions,

generating a recurrent reference signal in response to the operation ofthe cutter,

generating a recurrent waveform having a predetermined frequencyrelationship to said reference signal,

synchronizing the phase of.said recurrent waveform with the phase ofsaid varying portions of said density signal, irrespective of therelationship between said cutter and said dense regions at the instantsof severing the rod, and

correlating said recurrent waveform with one of said recurrent referenceand density signals to provide an output signal indicative of acharacteristic of said dense ends -in said plurality of cigarettes.

3. Apparatus for monitoring the operation of a cigarette-making machinehaving a cutter providing a plurality of cigarettes cut from acontinuous rod of tobacco moving along a path relative to said cutterand having locally dense regions spaced along said tobacco rod, saidapparatus having means for measuring the density of said tobacco rod asit passes a point along said path to generate a density signal having arecurrently varying portions corresponding to the said dense regions insaid moving rod, means responsive to the action of said cutter forgenerating a cutting signal, means for generating a recurrent waveform,and means for correlating said recurrent waveform with one of saiddensity and cutting signals to provide an output signal indicative of acharacteristic of said dense regions,

wherein said apparatus includes means for synchronizing the phases ofsaid density signal and said recurrent waveform, irrespective of thepositions of said dense regions with respect to said cutter at theinstant the rod is cut.

4. Apparatus for monitoring the operation of a cigarette-making machinehaving a cutter providing a plurality of cigarettes cut from acontinuous rod of tobacco moving along a path relative to said cutterand having locally dense regions spaced along said tobacco rod, saidapparatus comprising:

means for measuring the density of said tobacco rod as it passes a pointalong said path to generate a density signal having recurrently varyingportions corresponding to said dense regions in said moving rod,

means responsive to the action of said cutter for generating a cuttingsignal,

waveform generating means responsive to said cutting signal forgenerating a recurrent waveform in synchronized phase relationship withsaid varying portions of said density signal, and

means for correlating said recurrent waveform with said cutting signalto provide an output signal indicative of any displacement between thedense regions and the cut ends of the cigarettes.

5. Apparatus as set forth in claim 4, including means responsive to saidcutting signal for generating an additional recurrent waveform insynchronized phase relationship with said density signal, and

means for correlating said additional recurrent waveform with saiddensity signal to provide an additional output signal indicative of therelative density of said dense regions.

6. Apparatus as set forth in claim 4, including phase comparison meansfor correlating said recurrent waveform with said density signal toprovide a control signal indicative of the phase relationship betweensaid waveform and said density signal, and control means responsive tosaid control signal for maintaining said recurrent waveform in exactphase synchronization with said density signal.

7. Apparatus as set forth in claim 6, in which said control meansincludes means for triggering the operation of said waveform generatingmeans, and variable delay means responsive to said control signal andconnected to said triggering means, so that said waveform is triggeredin exact phase synchronization with said density signal.

8. Apparatus as set forth in claim 7, in which said variable delay meanscomprises a first information storage means for storing informationrelating to said control signal, a second information storage meansresponsive to said cutting signal and cycling through a plurality ofinformational states for each cigarette cut from the tobacco rod, and acomparison means responsive to both information storage means forcausing said triggering means to trigger said waveform generator togenerate said waveform at the frequency of said cutting signal and inexact phase synchronization with said density signal.

9. Apparatus as set forth in claim 8, in which said first and secondinformation storage means are digital registers and said comparisonmeans is adigital comparator.

10. Apparatus as set forth in claim 8, including an additional phasecomparison means for comparing the phase of said cutter signal withrespect to one of the informational states occurring during each cycleof. said second informational storage means, said additional phasecomparison means delivering an additional control signal indicative ofthe phase relationship betweensaid cutter signal and said reoccurringinformational state, said additional control signal controlling the rateat which said second informational storage means cycles through itsplurality of informational states.

11. Apparatus as set forth in claim 4, including output means responsiveto said output signal for providing said relationship between the denseregions and the cut ends of the cigarettes in the form of a visualindication.

12. Apparatus as set forth in claim 5, including output means responsiveto said additional output for providing a visual indication of therelative density of said dense regions.

13. Apparatus as set forth in claim 4, including a controller meansresponsive to said output signal for controlling the physicalrelationship between said cutter and said locally dense regions.

14. Apparatus as set forth in claim 4, in which said recurrent waveformis defined approximately by the equation f(l) =-f(t), with the originsof the time axis, t, and f(l) axis positioned so as to pass through thepoint midway between the lowest and highest values of a waveform period.

15. Apparatus as set forth in claim 14, in which said recurrent waveformis a sawtooth waveform.

16. Apparatus as set forth in claim 5, in which said additionalrecurrent waveform is defined approximately by the equation f(t) =f(t),with the f(t) axis positioned to coincide with the positive peakoccurring within a waveform period and the time axis, 1, positioned tocoincide with points midway along the slopes between the highest andlowest points of the waveform.

17. Apparatus as set forth in claim 16, in which said additionalrecurrent waveform is a triangular waveform.

18. Apparatus as set forth in claim 4, in which said correlating meanscomprises a sample-and-hold circuit.

19. Apparatus as set forth in claim 5, in which said correlating meanscomprises an analog multiplying circuit.

20. Apparatus as set forth in claim 6, in which said phase comparisonmeans comprises an analog multiplying circuit.

21. Apparatus for monitoring the operation of a cigarette-making machinehaving a cutter providing a plurality of cigarettes cut from acontinuous rod of tobacco moving along a path relative to said cutterand having locally dense regions spaced along said tobacco, saidapparatus comprising:

means for measuring the density of said tobacco rod as it passes a pointalong said path to generate a density signal having recurrent portionscorresponding to the said dense regions in said moving rod,

means responsive to the action of said cutter for generating a cuttingsignal,

first waveform generating means for generating a sawtooth-shapedrecurrent waveform,

means for sampling said sawtooth waveform with said cutting signal toprovide an output signal indicative of the phase relationship betweenthe dense regions and the cut ends of the cigarettes,

second waveform generating means for generating a triangular-shapedrecurrent waveform,

means for correlating said triangular waveform with said density signalto provide an output signal indicative of the percent density increasein tobacco in said dense regions,

phase comparison means for correlating said sawtooth waveform with saiddensity signal to provide a control signal indicative of the phaserelationship between said sawtooth waveform and said density signal,

an up/down counter responsive to said control signal for storing anumber representative of the phase relationship between said sawtoothwaveform and said density signal,

a cycling counter responsive to said cutting signal and cycling througha plurality of numbers for each cigarette cut from the tobacco rod,

a digital comparator responsive to said up/down counter and to saidcycling counter for generating an output pulse when one of the pluralityof numbers stored in said cycling counter equals the number stored insaid up/down counter,

means for triggering the operation of both said waveform generatingmeans, said means being responsive to the output pulse of said digitalcomparator,

additional phase comparison means for comparing the phase of said cuttersignal with respect to a particular one of the plurality of numbersstored in said cycling counter during each cycle, said additional phasecomparison means delivering an additional control signal indicative ofthe phase relationship between said cutter signal and said reoccurringparticular number, said additional control signal controlling the rateat which said cycling counter cycles through its plurality of numbers,and

output means responsive to said output signals for providing visualindications of said phase relationship and said percent densityincrease, respectively.

1. The method of producing an improved output response from a cigarettedense-end monitor, said monitor having means for measuring thevariations in density along the length of a rod of tobacco havinglocally dense regions spaced along said length for providing a densitysignal having recurrently varying portions corresponding to said denseregions in said rod, means for generating a recurrent signal waveformresponsive To the operation of a cutter which periodically cuts said rodto form individual cigarettes, and means responsive to said recurrentwaveform and to said density signal for providing said output responsewhich is indicative of a characteristic of said dense regions, saidmethod comprising adjusting the phase of one of said recurrent waveformand density signals in response to the recurrent waveform and densitysignals so that said signals will have a predetermined phaserelationship irrespective of the position of said dense regions withrespect to said cutter at the instant the rod is cut.
 2. The method ofmonitoring the operation of a machine for producing cigarettes withdense ends, said machine having means for forming a tobacco rod withlocally dense regions spaced along its length and means for conveyingsaid rod past a cutter for severing said rod into a plurality ofcigarettes, said method comprising the steps of measuring the variationsin density of said rod along its length to produce a density signalhaving recurrently varying portions thereof corresponding to said denseregions, generating a recurrent reference signal in response to theoperation of the cutter, generating a recurrent waveform having apredetermined frequency relationship to said reference signal,synchronizing the phase of said recurrent waveform with the phase ofsaid varying portions of said density signal, irrespective of therelationship between said cutter and said dense regions at the instantsof severing the rod, and correlating said recurrent waveform with one ofsaid recurrent reference and density signals to provide an output signalindicative of a characteristic of said dense ends in said plurality ofcigarettes.
 3. Apparatus for monitoring the operation of acigarette-making machine having a cutter providing a plurality ofcigarettes cut from a continuous rod of tobacco moving along a pathrelative to said cutter and having locally dense regions spaced alongsaid tobacco rod, said apparatus having means for measuring the densityof said tobacco rod as it passes a point along said path to generate adensity signal having a recurrently varying portions corresponding tothe said dense regions in said moving rod, means responsive to theaction of said cutter for generating a cutting signal, means forgenerating a recurrent waveform, and means for correlating saidrecurrent waveform with one of said density and cutting signals toprovide an output signal indicative of a characteristic of said denseregions, wherein said apparatus includes means for synchronizing thephases of said density signal and said recurrent waveform, irrespectiveof the positions of said dense regions with respect to said cutter atthe instant the rod is cut.
 4. Apparatus for monitoring the operation ofa cigarette-making machine having a cutter providing a plurality ofcigarettes cut from a continuous rod of tobacco moving along a pathrelative to said cutter and having locally dense regions spaced alongsaid tobacco rod, said apparatus comprising: means for measuring thedensity of said tobacco rod as it passes a point along said path togenerate a density signal having recurrently varying portionscorresponding to said dense regions in said moving rod, means responsiveto the action of said cutter for generating a cutting signal, waveformgenerating means responsive to said cutting signal for generating arecurrent waveform in synchronized phase relationship with said varyingportions of said density signal, and means for correlating saidrecurrent waveform with said cutting signal to provide an output signalindicative of any displacement between the dense regions and the cutends of the cigarettes.
 5. Apparatus as set forth in claim 4, includingmeans responsive to said cutting signal for generating an additionalrecurrent waveform in synchronized phase relationship with said densitysignal, and means for correlating said additional recurRent waveformwith said density signal to provide an additional output signalindicative of the relative density of said dense regions.
 6. Apparatusas set forth in claim 4, including phase comparison means forcorrelating said recurrent waveform with said density signal to providea control signal indicative of the phase relationship between saidwaveform and said density signal, and control means responsive to saidcontrol signal for maintaining said recurrent waveform in exact phasesynchronization with said density signal.
 7. Apparatus as set forth inclaim 6, in which said control means includes means for triggering theoperation of said waveform generating means, and variable delay meansresponsive to said control signal and connected to said triggeringmeans, so that said waveform is triggered in exact phase synchronizationwith said density signal.
 8. Apparatus as set forth in claim 7, in whichsaid variable delay means comprises a first information storage meansfor storing information relating to said control signal, a secondinformation storage means responsive to said cutting signal and cyclingthrough a plurality of informational states for each cigarette cut fromthe tobacco rod, and a comparison means responsive to both informationstorage means for causing said triggering means to trigger said waveformgenerator to generate said waveform at the frequency of said cuttingsignal and in exact phase synchronization with said density signal. 9.Apparatus as set forth in claim 8, in which said first and secondinformation storage means are digital registers and said comparisonmeans is a digital comparator.
 10. Apparatus as set forth in claim 8,including an additional phase comparison means for comparing the phaseof said cutter signal with respect to one of the informational statesoccurring during each cycle of said second informational storage means,said additional phase comparison means delivering an additional controlsignal indicative of the phase relationship between said cutter signaland said re-occurring informational state, said additional controlsignal controlling the rate at which said second informational storagemeans cycles through its plurality of informational states. 11.Apparatus as set forth in claim 4, including output means responsive tosaid output signal for providing said relationship between the denseregions and the cut ends of the cigarettes in the form of a visualindication.
 12. Apparatus as set forth in claim 5, including outputmeans responsive to said additional output for providing a visualindication of the relative density of said dense regions.
 13. Apparatusas set forth in claim 4, including a controller means responsive to saidoutput signal for controlling the physical relationship between saidcutter and said locally dense regions.
 14. Apparatus as set forth inclaim 4, in which said recurrent waveform is defined approximately bythe equation f(t) -f(-t), with the origins of the time axis, t, and f(t)axis positioned so as to pass through the point midway between thelowest and highest values of a waveform period.
 15. Apparatus as setforth in claim 14, in which said recurrent waveform is a sawtoothwaveform.
 16. Apparatus as set forth in claim 5, in which saidadditional recurrent waveform is defined approximately by the equationf(t) f(-t), with the f(t) axis positioned to coincide with the positivepeak occurring within a waveform period and the time axis, t, positionedto coincide with points midway along the slopes between the highest andlowest points of the waveform.
 17. Apparatus as set forth in claim 16,in which said additional recurrent waveform is a triangular waveform.18. Apparatus as set forth in claim 4, in which said correlating meanscomprises a sample-and-hold circuit.
 19. Apparatus as set forth in claim5, in which said correlatinG means comprises an analog multiplyingcircuit.
 20. Apparatus as set forth in claim 6, in which said phasecomparison means comprises an analog multiplying circuit.
 21. Apparatusfor monitoring the operation of a cigarette-making machine having acutter providing a plurality of cigarettes cut from a continuous rod oftobacco moving along a path relative to said cutter and having locallydense regions spaced along said tobacco, said apparatus comprising:means for measuring the density of said tobacco rod as it passes a pointalong said path to generate a density signal having recurrent portionscorresponding to the said dense regions in said moving rod, meansresponsive to the action of said cutter for generating a cutting signal,first waveform generating means for generating a sawtooth-shapedrecurrent waveform, means for sampling said sawtooth waveform with saidcutting signal to provide an output signal indicative of the phaserelationship between the dense regions and the cut ends of thecigarettes, second waveform generating means for generating atriangular-shaped recurrent waveform, means for correlating saidtriangular waveform with said density signal to provide an output signalindicative of the percent density increase in tobacco in said denseregions, phase comparison means for correlating said sawtooth waveformwith said density signal to provide a control signal indicative of thephase relationship between said sawtooth waveform and said densitysignal, an up/down counter responsive to said control signal for storinga number representative of the phase relationship between said sawtoothwaveform and said density signal, a cycling counter responsive to saidcutting signal and cycling through a plurality of numbers for eachcigarette cut from the tobacco rod, a digital comparator responsive tosaid up/down counter and to said cycling counter for generating anoutput pulse when one of the plurality of numbers stored in said cyclingcounter equals the number stored in said up/down counter, means fortriggering the operation of both said waveform generating means, saidmeans being responsive to the output pulse of said digital comparator,additional phase comparison means for comparing the phase of said cuttersignal with respect to a particular one of the plurality of numbersstored in said cycling counter during each cycle, said additional phasecomparison means delivering an additional control signal indicative ofthe phase relationship between said cutter signal and said re-occurringparticular number, said additional control signal controlling the rateat which said cycling counter cycles through its plurality of numbers,and output means responsive to said output signals for providing visualindications of said phase relationship and said percent densityincrease, respectively.